1. Field of the Invention
The present invention relates to nozzles, for cooling pistons of an internal combustion engine, which spray a cooling fluid such as oil onto the back of the piston, i.e. the face of the piston external to the combustion chamber, or in a piston tunnel.
2. Description of the Prior Art
The piston cooling nozzles usually employed are separate components, fixed to the engine housing and communicating with a cooling fluid feed orifice. The position of the nozzle is precisely determined to produce a jet of cooling fluid directed towards a precise area of the back of the piston or the piston tunnel.
Cooling nozzles generally include a valve to block the flow of cooling fluid until the pressure in the cooling circuit exceeds a particular threshold value.
Nozzle structures are generally employed in which the valve is a ball spring-loaded by a compression spring against a seat to shut off a cooling fluid passage. These structures are short and compact.
The inventors have found that the cooling nozzles with valves used until now operate correctly and prove satisfactory over a limited time period, after which wear interferes with the seal and correct operation of the valve. The period of correct operation decreases as the nominal pressure of the cooling fluid in the cooling pipes increases. Wear mainly modifies the opening characteristics of the valve, i.e. the fluid pressure required to open it: when new, the valve opens at a correct nominal pressure; when worn, the valve opens at a lower pressure, which can be as low as half the correct nominal pressure, and therefore at speeds below the engine idling speed. This interferes with the general pressure of the fluid in the engine.
The invention stems from the observation that the wear is inevitably caused by the structure of the ball valve itself: at high pressures the ball oscillates and vibrates, which causes the defects due to wear.
The document JP 07 317519 A discloses an engine cooling nozzle whose valve comprises a piston spring-loaded against a seat by a spring and sliding in an axial bore communicating with a radial fluid passage. The structure is long and bulky because opening of the valve necessitates movement and guidance of the piston downstream of the radial fluid passage.
The problem addressed by the present invention is that of designing a new structure for a nozzle incorporating a valve, and able to operate correctly over a significantly greater period of time, in particular without significant wear.
Surprisingly, the invention teaches that the ball valve can advantageously be replaced with a piston valve. Under similar conditions of use, at high pressure, a piston valve is not subject to the oscillation and vibration problems of ball valves, as a result of which satisfactory operation can be obtained over a significantly longer time period.
Another problem that the invention aims to solve is that of reducing the overall size of the nozzle within the engine cylinder. The piston valves from the document JP 07 317519 A yield a relatively large overall size, and in particular a relatively great length is required downstream of the outlet orifices of the valve for guiding the piston. An excessive length downstream of the outlet orifices of the valve leads to a risk of collision with rotating components of the engine such as the crankshaft or the crankshaft counterweight.
Accordingly, the invention aims to reduce the total length of the nozzle, and especially the length of the nozzle projecting into the engine cylinder downstream of the outlet structure with a radial fluid passage and an outlet tube.
To achieve the above and other objects, the invention provides a nozzle for cooling a piston of an internal combustion engine, including a nozzle body with a penetrating part shaped to engage in a bore of the engine and to receive a cooling fluid arriving via said bore, including an internal valve for modulating the flow of fluid as a function of its pressure, and including an outlet structure with a radial fluid passage in the nozzle body and an outlet tube, adapted to transmit cooling fluid leaving the internal valve and to direct it in the form of a jet at least against the back of the piston to be cooled; the internal valve includes a piston, having a downstream section with a cylindrical lateral guide surface sliding longitudinally in a guide bore in the nozzle body, having a head oriented in the upstream direction defined with respect to the direction of flow of the cooling fluid to bear selectively against an annular seat in the nozzle body and through which the cooling fluid flows, and the internal valve includes a compression coil spring, engaged axially between a downstream bearing surface in the nozzle body and a downstream surface of the piston to urge the piston in the upstream direction against the annular seat.
This kind of structure is very durable and very stable, which reduces oscillations and very significantly reduces wear phenomena.
According to the invention, the guide bore in which the piston slides is essentially inside an upstream section of the nozzle body, on the upstream side of the radial fluid passage, and fluid passages convey the fluid axially from the downstream side of the annular seat to the radial fluid passage as soon as the piston moves off the annular seat, so that, when the internal valve is open, the piston is substantially on the upstream side of the radial fluid passage.
The downstream section of the piston advantageously includes a downstream coaxial portion in which the upstream end part of the compression coil spring is engaged and guided.
In a first embodiment, the nozzle body has an axial through bore, in which is engaged without clearance and retained in position a tubular jacket with an axial bore, a downstream section of which forms the guide bore receiving the downstream section of the piston, the tubular jacket having an internal intermediate shoulder forming the annular seat, at least one radial hole being provided in the wall of the tubular jacket immediately downstream of the annular seat to convey fluid radially towards one or more peripheral passages between the external surface of the tubular jacket and the surface of the axial through bore of the nozzle body, said peripheral passages being adapted to convey cooling fluid axially from the radial hole or holes to the radial fluid passage in the nozzle body. In this way, when the valve is open, the piston is on the upstream side of the radial fluid outlet passage.
For example, the peripheral passage or passages comprise a larger diameter section of the axial through bore, whereas the tubular jacket has a substantially constant outside diameter leaving an annular intermediate space in which the cooling fluid flows.
It is preferable for the tubular jacket to be made of sintered steel, while the piston is made of steel. This considerably promotes sliding between the piston and the jacket, so reducing wear phenomena and the risks of binding.
In another embodiment, the piston includes, between its downstream section with its cylindrical lateral guide surface and the head, an external annular recess defining, with the wall of the guide bore, an annular housing communicating via radial piston holes with an axial piston bore open in the downstream direction into the axial passage through the body that conveys the cooling fluid to the radial fluid passage in the nozzle body. In this way, when the valve is open, the piston is well upstream of the radial fluid outlet passage.
The annular seat can be an annular ring mounted in the axial bore passing through the body of the nozzle.